Process for resisting corrosion by aliphatic acids



United States Patent PROCESS FOR RESISTIN G CORROSION BY ALIPHATIC ACIDS Alfred Frank Millidge, Coulsdon, and Ian Kenneth Miles Robson, Clapham Common, London, England, assign- 'ors to The Distillers Company Limited, Edinburgh,-

Scotland, a British company No Drawing. Application October 25, 1954 Serial No. 464,636.

' Claims priority, application Great Britain October 31, 1953 2 Claims. (Cl. 202-59).

The present invention relates to the treatment of organic acid mixtures containing formic acid, more particularly those obtained by the oxidation of organic compounds. f

In operations involving the treatment of organic acids,

such as distillation operations, it is necessary to use corhave shown (Lane, Golden and Acheman, Industrial &

Engineering Chemistry, 1953, volume 45, page 1067), that the corrosion of stainless steel by hot formic acid is a maximum in the presence of air and a minimum in theabsence of air, and these findings have been verified by the applicants.

It is an object of the present invention to. provide a process involving the heat treatment of aliphatic acids obtained by the oxidation of hydrocarbons or ketones, containing formic, acetic and other acids, in apparatus constructed at least in part of stainless steel, in which the corrosion of stainless steel is reduced to a minimum.

Accordingly the present invention is for a process involving the heat treatment in apparatus constructed at least in part of stainless steel, of a mixture of aliphatic acids including a minor proportion of formic acid obtained by the oxidation with molecular oxygen of hydrocarbons or ketones which comprises passing an oxygen containing gas through the mixture during the heat treatment.

The heat treatment involved is most usually a distillation operation. The process of the invention however isnot restricted to distillations, but may equally be applied to other operations involving the heat treatment of mixtures of aliphatic acids.

The mixture of aqueous aliphatic acids containing a minor proportion of formic acid generally comprises an aqueous mixture of formic, acetic, propionic and butyric acids wherein the formic acid content is less than about 25% by weight of the mixture. Such acid mixtures are obtained for example by the processes described in copending U.S. applications Ser. Nos. 385,272; 385,182 and 385,306 which relate to the production of aliphatic acid by the oxidation of lower paraiiinic hydrocarbons. In such oxidations, ketones such as acetone and methyl ethyl ketone are intermediate products and accordingly ketones may serve as starting materials in the oxidation reaction to produce the mixture of aliphatic acids to be treated according to the invention. The oxidation product is usually submitted to a series of distillation steps to re: cover the acids, and the invention is'us'eful with any of the acid containing mixtures so obtained, as well as with, the oxidation product itself. Even during the distillation of formic acid from higher acids, the invention may beused to reduce corrosion in atle'ast the base of the still and the lower parts of the column.

The stainless steel employed in the construction of the apparatus used in the process of the invention may be any of the stainless steels which are available. Such steels are the nickel-chromium steels for example Firth Vickers FMB containing 18% chromium, 8.5% nickel, 2.75%

molybdenum and FDP containing 18% chromium, 8.5

nickel, 0.6% titanium and like steels.

The oxygen containing gas may comprise oxygen, air, ozone or the like. economical to employ air as the oxygen containing gas.

The oxygen containing gas is most conveniently passed through the mixture by passing a stream of the gas in at the base of the apparatus and withdrawing the gas at some point at the top of the apparatus.

The following examples are given to illustrate the process of the present invention.

Example 1 Two strips of stainless steel containing 18% chromium, 8% nickel were partially immersed in a mixture of wet acids, obtained by the oxidation of paratfin hydrocarbons of 4-8 carbon atoms, and removal of lightand heavy ends, of the composition? Percent by weight Water 28 Formic acid 11 Acetic acid 54 Propionic acid Butyric acid 1 1 Neutrals 1 at the boiling point -105.), in two separate vessels;

through one vessel a very slow stream of air was passed, through the other a very slow stream of nitrogen. corrosions produced were as follows:

Example 2 A strip of stainless steel containing 18% chromium, 8.5% nickel, 0.6% titanium was partially immersed in wet acids, obtained by the oxidation of parafiin hydrocarbons, of the composition: I

Percent by weight Water 28 Formic acid l1 C to C acids 60 Neutrals 1 at the boiling point (100105 while a very slow stream of ozonized oxygen was passed in. The corrosion produced, over a period of 7 days, corresponded to a penetration rate of 0.0001 inch/year.

Example 3 The corrosions produced on two samples of stainless It is generally most convenient and p The Corrosion Penetration steel were determined-by a-dynamicmethod. The-strips were whirled, at a peripheral speed of 7.1 feet/second, through boiling wet acids, obtained by the oxidation of paraflin hydrocarbons, of the composition:

Percent by weight Water" v .2 Formic acid 11 Cgto C4 acids V 60' Neutrals 1,

a tslowlstream otair wasinjected initially, andwas subseqtlfintly changed tonne-ofnitrogen. The great increase in corrosion bro'ughtabout inthe-absence of air I is: shown; in the following, table;

Corrosion Penetration (incheSX10- /year) Grade-of stainless steel sltqrip 0.,

- Example 4 Stainless-steel corrosio-n strips were;,-placed in thekettle of a glass continuous; still employed for topping a parafiinic hydrocarbon oxidate of composition:

Percent by Weight Water 20 Formic acid 4.5 Cg. toEC acids.. 25.5 Neutralsf 45 Higher acids and highers 5 In the first two periods of operation-av slow stream-of nitrogen waswblown into the kettle of the still, and taken olf'fatthestillhead; in the last two periods a. slow stream ofvairwassubstituted forthe nitrogen. The advantageous efiectsproducedbyvthe presence of air are shown in .thefollowingtable:

Corrosion Penetration Example '5 Stainless-5steelcorrosion strips were placed in the kettle, at the;feed point-and'in the stillhead of a glass continuouszstill employed for topping a wet acid mixture, obtained by the oxidation of .paraffin hydrocarbons of the composition: 7

. Percent by weight Water 28 Forrnic acid 11 C to C acids 60 Neutrals 1 A; slow streanrof air was blown ,into thekettle ofrthe 4. still and taken ofiE-at the stillhead. The corrosions-measeured are shown in the following table:

Corrosion Penetration (inchesX10 year) Grade of stainless steel Position of strip Period 1 Period 2 .(2 ys) (New) feedpoint 0. 0 5. 4 Firth Vickers FDP u, kettle-totally submerged; 1 0. 12., 0.0 1'.

arr-ne n s 3*8' a e eo a ysu merge Firth Vic-mills {kettle-partly submerged; 0.10 0.0

Examri le Stainless steel corrosiontstripswere immersed in the stated liquids at theboiling point forperiodseach of 1 week duration. The wet acidswere obtained by the oxidation of a parafiinic fraction of boiling range 15 -95.

C., and had approximately the same composition as the wet acids employed in Example 3.

Corrosion Penetration 7 (inehesXlWb/year). Corroding Liquid Cover u Period Period Period I air. I 0.1 1111. m1. Wet {nitrogen 15.0 9:1 4. iFormicAcid (Anelytical Re- {air 14.7 9. 4 19, Aagent Gfi ade Q8"1&()Q(/15)( A l nitrogen 3. 4 9:0 8.

queens ormie or nay 1-' cal Reagent Grade-73%by}% .5' 7" 2-3; woight-l-water27%byweight). g

We claim:

1. A process involving the heat treatment inapparatusa constructed in major part of stainless steel,,of,a,mixture ofaliphaticacids obtained by the oxidationwith nnit 1:v ular oxygen-of a substance selected from-thegroupcomsisting of, hydrocarbons andnketones, which comprises; passing molecular oxygen through;v the mixture contain: ing not more than 25% formic acid while. in contact. with saidstainless, steel during the heat treatment to inhibit corrosion of said stainless steel. 4

2. A process involving the heat treatmentin apparatttis,v constructed in major part .ofstainless steel, of.-'a,rm'x ture of aliphatic acidswhose carbon chains havenot over 4 v carbon atoms, obtainedby the oxidation withmoleculars; oxygen of a substanceselected fromthe.groupv consisting ofv hydrocarbons and ketones, which comprises passing molecular oxygen. through the mixture contain-.. ing not over. 11% formic. acid while incontactawith, said stainless steel during the heat treatment .torinhibit corrosion of said stainless steel.

References Cited in the file of this patent UNITED STAT ES. PATENTS;

' OTHER REFERENCES Chemical Engineers; Handbook? Perry. (McGraw-.: Hill, 3rd ed., 1950), p. 1458. (Copy in' ScientifioLibz) 1 

